Acoustic wave devices having piezoelectric thin film resonators have been used as filters and duplexers of wireless devices such as, for example, mobile phones. The piezoelectric thin film resonator has a multilayered structure in which a lower electrode and an upper electrode face each other across a piezoelectric film. The region where the lower electrode and the upper electrode face each other across the piezoelectric film is a resonance region. An air gap reflecting the acoustic wave is formed under the lower electrode in the resonance region as disclosed in, for example, Japanese Laid-open Patent Publication Nos. 2013-038658, 2005-347898, and 2015-095714 (hereinafter, referred to as Patent Documents 1 through 3, respectively). There has been known a structure in which the piezoelectric film has a lower piezoelectric film and an upper piezoelectric film and the outer periphery of the lower piezoelectric film is located further out than the outer periphery of the upper piezoelectric film as disclosed in, for example, Patent Document 1.